The long-range goal of this research is to examine the role of H,K-ATPases in potassium homeostasis and to determine how these ion-motive pumps are regulated by ion channels. H,K-ATPases are important for renal potassium conservation, but it is now apparent that the kidney possesses several different H,K-ATPase enzymatic activities which likely reflect the presence of multiple gene products. Experiments in Specific Aim 1 will determine the molecular identities of the H,K-ATPase subunit isoforms that are responsible for specific enzymatic activities, and for potassium and proton flux in discrete nephron segments, by the study of animals with targeted gene disruption of the H,K-ATPase HK-alpha-1, HK-alpha-2, or HK-beta genes. Experiments in Specific Aim 2 will examine whether knockout of HK-alpha-1, HK-alpha-2, or HK-beta subunits affects the normal anatomy of the kidney or the morphological response to potassium depletion. Experiments in Specific Aim 3 will characterize fully the newly discovered potassium-permeable ion channels that are present at the apical membrane of the inner stripe of the outer medullary collecting duct (OMCD), and the cell types that contain these channels. These channels exhibit novel properties since they appear to be stimulated by cellular acidification whereas most potassium channels are inhibited by acidosis. The proposed experiments are intended to establish the contribution of each of these genes to an important adaptive response (potassium depletion), the compensatory renal response to the disruption of these genes, and whether these genes are involved in the normal morphology of the kidney or its response to potassium depletion. Since accruing evidence indicates that modest potassium depletion causes or contributes to systemic arterial hypertension, and may contribute to chronic renal insufficiency, these studies area expected to contribute to our understanding of the role of potassium depletion as a risk factor for both renal and cardiovascular disease.